I've got a "new" iPhone 11 and I'm new to iOS. My previous smartphone was an Android phone and I used to sync my photos with NextCloud for Android. So I've now installed NextCloud for iOS and marked my folders as available when offline, assuming that is how you download your photos to your iPhone with NextCloud (I've verified in airplane mode that NextCloud can open the photos, so the photos are actually there in the iPhone memory, somewhere).
After it finished downloading, in the Photos app I only see a "NextCloud" folder which contains only a text file (a log of what NextCloud downloaded), but no pictures. However, since I can see my photos in the NextCloud app for iOS even when I activate airplane mode, I'm pretty sure they are there, but I suspect that there is non where the Photos app assumes them to be. But I might also be wrong, so please don't take my word on that.
What should I do to have my photos show up in Photos?